I am massively confused. Doesn't Einstein's theory of general relativity say something along the lines that there is no gravity, it's just curvature in spacetime due to objects in the universe? Why would Einstein coin a theory of Gravitational waves if gravity didn't exist? Are waves just curves that wobble? And do the gravitational waves detected by the LIGO wibbly wobbly detector disprove the existence of Einstein?

Robin Laurén asked the Naked Scientists: I am massively confused. Doesn't Einstein's theory of general relativity say something along the lines that there is no gravity, it's just curvature in spacetime due to objects in the universe? Why would Einstein coin a theory of Gravitational waves if gravity didn't exist? Are waves just curves that wobble? And do the gravitational waves detected by the LIGO wibbly wobbly detector disprove the existence of Einstein?

What do you think?

Einstein never claimed that Gravity did not exist. He only claimed that Gravity is an effect brought about by the curvature of Spacetime, as opposed to Gravity being a force transmitted by a force carrier particle like a graviton. Spacetime exists and can be curved, twisted, stretched and compacted. Now that curvature can be made to travel out from a source as waves in the physical but not particle based Spacetime. They are called Gravity Waves because they employ the "matter - Spacetime" interaction of mass manipulating the physical nature of spacetime.

« Last Edit: 25/02/2016 08:32:52 by chris »

Logged

We are made of Spacetime; with a sprinkling of Stardust.Matter tells Spacetime how to Flow; Spacetime tells matter where to go

We can view gravity as a "field" that permeates space - the gravitational field.

In the vicinity of the Sun, this gravitational field takes on more extreme values, so that you have to use a powerful rocket to get from Earth to Pluto (further away from the Sun). This effect is due to the mass of the Sun, bending space-time.

As a result of this gravitational field, the planets follow elliptical orbits around the Sun.

Quote from: John Wheeler

Mass tells space-time how to curve, and space-time tells mass how to move.

This "steady" gravitational field around the Sun and Earth follows Newton's laws very closely - you have to look very closely at the orbit of Mercury to see a very small divergence from Newton's gravity. (This small effect is due to time dilation. Gravitational waves, which are the subject of this thread are far more subtle again.)

However, one implication of Einsteins General Theory of Relativity (published a year later, in 1916) was that if you have very intense accelerating gravitational fields (such as surround closely orbiting black holes or neutron stars), some of the orbital energy is carried away as "ripples" on the gravitational field. This is what we call gravitational waves.

The 1993 Nobel prize in Physics was awarded for discovering a pulsar (in a pair of neutron stars) whose orbit reflects Einsteins prediction. The LIGO team are hoping they will win another one....

Gravitational waves are not totally strange. We are familiar with another field that permeates space - the electromagnetic field. You can have a "steady" field from a battery or a bar magnet. Or you can accelerate the electric charges, which causes "ripples" on the electromagnetic field, carrying energy away from the source. This was predicted by Maxwell, and we now call it radio, X-Rays and light. Maxwell's work laid some of the foundations for Einstein's work.

Quote from: Robin Lauren

And do the gravitational waves detected by the LIGO wibbly wobbly detector disprove the existence of Einstein?

They don't change the existence of Einstein the man, or his theory. Assuming this observation holds up to further scrutiny:

What he got right: Gravitational waves do exist (but we've sort of known that since 1993; this gives direct detection of it)

Another thing he got right: The effect is very subtle. We are talking about displacements of less than the diameter of a proton in 4km.

One thing he got wrong: He thought the effect was so subtle that we would never detect them. It took 100 years of technological advance, spending a billion dollars, and the existance of black holes (they have a very intense gravitational field; Einstein wasn't entirely sure such things could exist, since his theory started producing infinities when you got too close).

late to this one but no. Einstein did not think of it as a geometry. He thought of it as a relativistic gravitational 'field'. In a similar way to how you can change your experience of a Electromagnetic field by your 'motion' relative it, a gravitational field also is observer dependent. It exist as long as you don't fall, as soon as you're in that free fall you negated it acting on you, locally defined. So he wanted to find a way to unify both into one field, as I understand it.

late to this one but no. Einstein did not think of it as a geometry. He thought of it as a relativistic gravitational 'field'. In a similar way to how you can change your experience of a Electromagnetic field by your 'motion' relative it, a gravitational field also is observer dependent. It exist as long as you don't fall, as soon as you're in that free fall you negated it acting on you, locally defined. So he wanted to find a way to unify both into one field, as I understand it.

Did he ever come around to thinking of it as a geometry?

I know he was unhappy with Minkowski diagrams but later was happy with them....is that a very different case?

I think you said earlier that he tried to unify gravitation theory with the other forces. Is this attempt still ongoing or is the prevailing consensus(if it exists) that gravity is entirely different from them?

I do not agree with the idea that general relativity is geomterizing physics of a gravitational field. The concepts of physics have always been geometrical concepts and I cannot see why the gik field should be called more geometrical han f.i. the electromagnetic field or the distance between bodies in Newtonian mechanics. The notion probably comes from the fact that the mathematical origin of the gik[/dub] field is the Gauss-Riemann theory of the metrical continuum which we are wont to look at as part of geometry. I am convinced, however, that the distinction between geometrical and other kinds of fields is not logically founded.

Doesn't Einstein's theory of general relativity say something along the lines that there is no gravity, it's just curvature in spacetime due to objects in the universe?

No. It says that tidal gradients in a gravitational field is another term of spacetime curvature. GR interprets the gravitational force as an inertial force, i.e. a force only apparent from a non-inertial frame of reference. He considered such forces as being real whereas most physicists today don't, i.e. they disagree with Einstein.

I do not agree with the idea that general relativity is geomterizing physics of a gravitational field. The concepts of physics have always been geometrical concepts and I cannot see why the gik field should be called more geometrical han f.i. the electromagnetic field or the distance between bodies in Newtonian mechanics. The notion probably comes from the fact that the mathematical origin of the gik[/dub] field is the Gauss-Riemann theory of the metrical continuum which we are wont to look at as part of geometry. I am convinced, however, that the distinction between geometrical and other kinds of fields is not logically founded.

Were there any practical consequences to this disagreement?Is it simply a matter of interpretation ?

When theoretical physicists explore possible versions of a quantum gravity do these interpretations assume a greater importance?

Am I right to assume ** that the curvature of spacetime does not feature in any of the current (successful) quantum theories ?

**clearly I can only assume when I have very little personal understanding of those theories....